Kepler-186 is a

main-sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hert ...

M1-type

dwarf star A dwarf star is a star of relatively small size and low luminosity. Most main sequence stars are dwarf stars. The meaning of the word "dwarf" was later extended to some star-sized objects that are not stars, and compact stellar remnants which are ...

, located 178.5

parsecs The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

(582 light years) away in the constellation of Cygnus. The star is slightly cooler than the

sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

, with roughly half its

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...

. It is known to have five planets, including the first Earth-sized world discovered in the

habitable zone In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kas ...

Kepler-186f Kepler-186f (also known by its Kepler object of interest designation KOI-571.05) is an exoplanet orbiting the red dwarf Kepler-186, about from Earth. It was the first planet with a radius similar to Earth's to be discovered in the habitable ...

. free version = http://www.nasa.gov/sites/default/files/files/kepler186_main_final.pdf The star hosts four other planets discovered so far, though they all orbit interior to the habitable zone.

Star

A number of previously unknown measurements of the star are known.VizieR Detailed Page
for 2MASS 19543665+4357180, "This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation." In the infrared/microwave EM spectrum its H band magnitude is 11.605, J band magnitude is 12.473, and its K band magnitude is 11.605. In the visual

Photometric system In astronomy, a photometric system is a set of well-defined passbands (or optical filters), with a known sensitivity to incident radiation. The sensitivity usually depends on the optical system, detectors and filters used. For each photometric sy ...

magnitude it is 14.90(R)(towards the red end of the visual spectrum) and 16.40(B)(the blue end of the spectrum) (see also

Apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...

.) It is a

BY Draconis variable BY Draconis variables are variable stars of late spectral types, usually K or M, and typically belong to the main sequence. The name comes from the archetype for this category of variable star system, BY Draconis. They exhibit variations in the ...

changing brightness slightly, probably from star-spots, with a period of 33.695 days. The star is an M-type

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...

, bordering on being a K-type

orange dwarf A K-type main-sequence star, also referred to as a K-type dwarf or an orange dwarf, is a main-sequence (hydrogen-burning) star of spectral type K and luminosity class V. These stars are intermediate in size between red M-type main-sequence stars ...

, with a mass 0.544 times that of the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

's and a density of .

Discovery of a planetary system

Within two first years of gathered data, the signals of four inner planetary candidates were found. Discussion of planets in the system was taking place in August and November 2013. See comment by "Holger 16 November 2013 at 14:21".
^
^
^ In February 2014, those planets were confirmed through the "verification by multiplicity" method. The fifth outermost candidate was confirmed in the same manner in April 2014. The possibility that the signals in the light curve of the star were actually from something else has been ruled out by an investigation with the W. M. Keck and Gemini Observatories, using

speckle imaging Speckle imaging describes a range of high-resolution astronomical imaging techniques based on the analysis of large numbers of short exposures that freeze the variation of atmospheric turbulence. They can be divided into the shift-and-add ("'' ...

and

adaptive optics Adaptive optics (AO) is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical tele ...

techniques, which, while unable to resolve the planets, were able to rule out other possibilities than the system of planets.

Planetary system

The five planets discovered around Kepler-186 are all expected to have a solid surface. The smallest one, Kepler-186b, is only 8% larger than Earth, while the largest one, Kepler-186d, is almost 40% larger. The four innermost planets are probably

tidally locked Tidal locking between a pair of co-orbiting astronomical body, astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where ...

, but Kepler-186f is farther out, where the star's tidal effects are much weaker, so there may not have been enough time for its spin to slow down that much. Because of the very slow evolution of red dwarf stars, the age of the Kepler-186 system is poorly constrained, although it is likely to be greater than a few billion years. There is a roughly 50-50 chance it is tidally locked. Since it is closer to its star than Earth is to the Sun, it will probably rotate much more slowly than Earth; its day could be weeks or months long (see Tidal effects on rotation rate, axial tilt and orbit). Planetary formation simulations have also shown that there could be one additional non-transiting low-mass planet between Kepler-186e and Kepler-186f. If this planet exists, it is likely not much more massive than Earth. If it were, its gravitational influence would likely prevent Kepler-186f from transiting.Formation, tidal evolution and habitability of the Kepler-186 system
Emeline Bolmont, Sean N. Raymond, Philip von Paris, Franck Selsis, Franck Hersant, Elisa V. Quintana, Thomas Barclay, (Submitted on 16 Apr 2014) Conjectures involving the

Titius–Bode law The Titius–Bode law (sometimes termed just Bode's law) is a formulaic prediction of spacing between planets in any given solar system. The formula suggests that, extending outward, each planet should be approximately twice as far from the Sun as ...

, (and the related Dermott's law) indicate that there could be several remaining planets to be found in the system - two small ones between e and f and another larger one outside of f. That hypothetical outer planet must have an orbital radius beyond 16.4 AU for planetary system to remain stable. The low

of the star at a metallicity (dex) of -0.26, or to put it another way, about half that of the Sun's, is associated with a decreased chance of planets overall and giant planets specifically but an increased chance of Earth sized planets, in a general study of stars.

Naming

Kepler project

As the

Kepler telescope The Kepler space telescope is a disused space telescope launched by NASA in 2009 to discover Earth-sized planets orbiting other stars. Named after astronomer Johannes Kepler, the spacecraft was launched into an Earth-trailing heliocentric orbit ...

observational campaign progressed initial identifications of systems were entered in the

Kepler Input Catalog The Kepler Input Catalog (or KIC) is a publicly searchable database of roughly 13.2 million targets used for the Kepler Spectral Classification Program (SCP) and ''Kepler''. Overview The Kepler SCP targets were observed by the 2MASS project ...

(KIC), and then progressed as a candidate host of planets as Kepler Object of Interest (KOI). Thus Kepler 186 started as ''KIC 8120608'' and then was identified as ''KOI 571''.

Outside the Kepler project

Outside of the Kepler project, the

2MASS The Two Micron All-Sky Survey, or 2MASS, was an astronomical survey of the whole sky in infrared light. It took place between 1997 and 2001, in two different locations: at the U.S. Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona, and ...

survey catalogued this star as ''2MASS J19543665+4357180''.

References

External links

First Potentially Habitable Terran World
PHL
NASA's Kepler Discovers First Earth-Size Planet In The 'Habitable Zone' of Another Star
NASA, April 17, 2014
Kepler-186 at The NASA Exoplanet Archive
{{Stars of Cygnus, state=collapsed

571 __NOTOC__ Year 571 ( DLXXI) was a common year starting on Thursday (link will display the full calendar) of the Julian calendar. The denomination 571 for this year has been used since the early medieval period, when the Anno Domini calendar er ...

M-type main-sequence stars Cygnus (constellation) Planetary systems with five confirmed planets J19543665+4357180 Planetary transit variables TIC objects